In mining operations, holes are frequently drilled into the walls, floor, and/or roof of the mine passages to plant explosives to fracture the rock. Holes are also drilled for setting bolts to stabilize the rock surfaces of the mine passages. A rock drilling machine such as a rock drill jumbo or a roof bolter is usually employed for such drilling operations.
The rock drilling machine typically has a feed shell positioning mechanism which includes a boom which is attached to a carrier vehicle which is used to mobilize the boom. One example of such a boom and carrier vehicle is shown in U.S. Pat. No. 5,556,235, assigned to the assignee of the present application. FIGS. 1 through 5 illustrate exemplary prior art feed shell positioning mechanisms.
FIGS. 1 and 2 illustrate respectively a side view and an end view of a prior art feed shell positioning mechanism 10 which is mounted to a boom 12. The boom 12 is attached to a carrier vehicle (not shown) which serves to transport the feed shell positioning mechanism 10 to the rock surface. A feed shell support 14 is pivotably and rotatably mounted with respect to the boom 12. A feed shell 16, having a longitudinal feed shell axis 18, slidably engages the feed shell support 14. A feed shell advancing actuator 20 is employed as a means for advancing the feed shell 16 toward a rock surface to be drilled.
The boom 12 usually has attached thereto a horizontal wrist joint 22 and a vertical wrist joint 24. The wrist joints (22 and 24) permit the feed shell 16 to be tilted relative to the boom 12. The wrist joints (22 and 24) permit adjustment of the feed shell 16 with respect to the boom 12 so that a series of parallel holes can be drilled as the boom 12 is moved. It should be noted that any pair of wrist joints or a universal joint which acts in substantially normal planes could be employed to allow drilling parallel holes as the boom 12 is moved; however, having both a horizontal and a vertical wrist joint simplifies the description of the geometry, and such a configuration will be used for describing embodiments discussed in the application.
To provide further flexibility in the positioning of the feed shell 16, the feed shell positioning mechanism 10 includes a roll actuator 26 having a roll actuator axis 28. The roll actuator 26 is connected to the boom 12, having the wrist joints (22 and 24) interposed therebetween. The roll actuator 26 provides a means of rotation about the roll actuator axis 28 and increases the adjustability of the feed shell 16. A variety of rotary actuators are commercially available such as Helac.RTM. helical rotary actuators. Helical rotary actuators are further described in U.S. Pat. No. 4,422,366.
Helical rotary actuators provide a large angular displacement between a radially internal output shaft, which in the roll actuator 26 illustrated is affixed to the boom 12, and a housing, which is rotated about the roll actuator axis 28.
The feed shell positioning mechanism 10 also has a rock drill 30, which is advancable along the feed shell 16. The rock drill 30 has a drill axis 32, which is parallel to the feed shell axis 18. The feed shell axis 18 and the drill axis 32 define a reference plane 34.
A swivel assembly 36 is interposed between the roll actuator 26 and the feed shell support 14. The swivel assembly 36 has a roll actuator securing element 38 attached to the roll actuator 26. A feed shell support securing element 40 is attached to the feed shell support 14. The feed shell support securing element 40 pivots relative to the roll actuator securing element 38 about a swivel axis 42. The swivel axis 42, for the positioning mechanism illustrated, is parallel to the reference plane 34, as can be best seen in FIG. 2.
The swivel assembly 36 also includes a swivel activation means for pivoting the roll actuator securing element 38 with respect to the feed shell support securing element 40. The swivel activation means serves to pivot the feed shell support 14 about the swivel axis 42 to move the feed shell 16 and the rock drill 30 between a forward drilling orientation, illustrated in FIGS. 1 and 2, and a sideways drilling orientation, illustrated in FIGS. 3 and 4. In the feed shell positioning mechanism 10 illustrated in FIGS. 1 through 4, the swivel activation means is provided by a hydraulic cylinder 44 which is pivotably mounted to the roll actuator securing element 38 and is also pivotably mounted to the feed shell support securing element 40.
In the forward drilling orientation, the feed shell axis 18 is substantially parallel to the roll actuator axis 28. In the sideways drilling orientation, the feed shell axis 18 is substantially normal to the roll actuator axis 28. It will be noted that, when the roll actuator 26 is positioned such that the feed shell 16 is co-planar with the boom 12 in a vertical plane and the roll actuator axis 28 is in a horizontal plane, the feed shell axis 18 remains horizontal as the feed shell support 14 is swivelled between the forward drilling orientation and the sideways drilling orientation.
FIG. 5 illustrates an alternative prior art feed shell positioning mechanism 10', which employs a swivel assembly 36' where the swivel axis 42' is perpendicular to the reference plane 34'. In the feed shell positioning mechanism 10', the boom 12 does not reside in the reference plane 34' when the feed shell 16 is in the forward drilling orientation, as occurs with the feed shell positioning mechanism 10 illustrated in FIGS. 1 through 4. Rather, the boom 12 is offset from the reference plane 34' to avoid interference. In the feed shell positioning mechanism 10', the feed shell 16 pivots such that the feed shell axis 18 is roughly vertical when the feed shell 16 is swivelled into the sideways drilling orientation, as is shown in phantom.
The offset of the boom 12 with respect to the reference plane 34 when the feed shell 16 is in the forward drilling orientation avoids interference between the feed shell 16 and the boom 12 as the vertical wrist joint 24 is used to tilt the feed shell 16 relative to the boom 12.
However, having the boom 12 offset with respect to the reference plane 34 when the feed shell 16 is positioned in the forward drilling orientation is generally undesirable, since it makes positioning the rock drill 30 difficult in corners. In corners, interference of the boom 12 with a sidewall may prevent positioning the rock drill 30 in locations in close proximity to the sidewall. This typically requires the roll actuator 26 to be used to rotate the feed shell 16 to the side of the boom 12 near the sidewall, which interrupts work while the feed shell 16 is repositioned, and also results in the feed shell 16 and rock drill 30 being inverted, which interferes with visibility for the operator.
To avoid the problems which result from offsetting the feed shell 16, it is generally preferred to center the feed shell 16 over the boom 12, such that the boom 12 resides in the reference plane 34 when the feed shell 16 is in the forward drilling orientation, as is the case with the feed shell positioning mechanism 10 illustrated in FIGS. 1 through 4. When the feed shell 16 is so positioned, it is desirable to have a large separation between the feed shell axis 18 and the roll actuator axis 28. This large separation allows the vertical wrist joint 24 to tilt the feed shell 16 relative to the boom 12 in the reference plane 34 over a fairly large range without the feed shell 16 interfering with the boom 12. Similarly, if the roll actuator 26 is activated to position the feed shell,16 alongside the boom 12, the large separation allows the horizontal wrist joint 22 to angle the feed shell 16 relative to the boom 12 in a horizontal plane without interference.
Positioning the feed shell 16 over the boom 12 and providing a large separation S between the drill axis 32 and the roll actuator axis 28 is desirable for forward drilling, since it provides a large separation between the boom 12 and the feed shell 16. However, a large separation S between the drill axis 32 and the roll actuator axis 28 is undesirable when the feed shell 16 is pivoted from the forward drilling orientation to the sideways drilling orientation. In the sideways drilling orientation, when the separation S between the drill axis 32 and the roll actuator axis 28 is large, the large separation S results in undesirably large torsional loads on the boom 12, the roll actuator 26, and the swivel assembly 36.
Thus, there is a need for a feed shell positioning mechanism which has the feed shell centered with respect to the boom and where there is a small separation between the drill axis and the roll actuator axis when in the sideways drilling orientation, while still maintaining a large separation between the feed shell and the boom in the forward drilling orientation.